Skeletal Muscle Contraction and Function Overview

11 steps of skeletal muscle contraction

Nerve signal → ACh release → ACh binds → EPP → Action potential → Ca²⁺ release → Ca²⁺ binds troponin → Tropomyosin moves → Myosin binds → Power stroke → ATP detachment/reset

Causes of muscle relaxation after contraction

ACh broken down, Ca²⁺ pumped back to SR, tropomyosin covers actin, muscle relaxes

5 functions of skeletal muscle

Movement, posture, protection, elimination, heat production

What surrounds each muscle fiber?

Endomysium

Order muscle structures from largest to smallest

Muscle → Fascicle → Fiber → Myofibril → Myofilament

What is the sarcolemma?

The muscle cell membrane

Function of T-tubules

Carry signal deep into muscle fiber

What does the sarcoplasmic reticulum do?

Stores and releases calcium

What does the Na⁺/K⁺ pump do?

3 Na⁺ out, 2 K⁺ in, uses ATP

What proteins are in thin filaments?

Actin, tropomyosin, troponin

5 parts of a sarcomere

Z-line, I-band, A-band, H-zone, M-line

What is a motor unit?

One motor neuron + all muscle fibers it controls

3 parts of a neuromuscular junction

Synaptic knob, synaptic cleft, motor end plate

3 energy systems of muscle metabolism

Phosphagen, anaerobic respiration, aerobic respiration

3 sources of ATP in the phosphagen system

Stored ATP, creatine phosphate, ADP + ADP via myokinase

Anaerobic vs aerobic: which is faster and which yields more ATP?

Anaerobic = fast, low ATP; Aerobic = slow, high ATP

Which muscle fiber type is fatigue-resistant?

Slow oxidative (Type I)

What is the latent period in a muscle twitch?

Delay between stimulus and contraction

Difference between isometric and isotonic contractions

Isometric = no length change; Isotonic = length changes

One cause of muscle fatigue

Glycogen depletion (or others: Pi buildup, less Ca²⁺, etc.)

Which muscle types are striated?

Skeletal and cardiac

What is hypertrophy?

Increase in muscle cell size

Where is smooth muscle found?

Walls of hollow organs like stomach, intestines, blood vessels

What replaces sarcomeres in smooth muscle?

Dense bodies

One major difference between skeletal and smooth muscle contraction

Smooth uses calcium from outside the cell too; contraction is slower but lasts longer

What does the deltoid do?

Abducts the arm

What's the movement when you raise your arm out to the side?

Abduction

What does creatine phosphate do in muscle cells?

Quickly makes ATP by donating a phosphate

What does sodium do during muscle contraction?

Enters the cell to start the action potential

What's the role of acetylcholine (ACh)?

Neurotransmitter that activates muscle contraction